~ I run Chevron Supreme in the Coupé with an occasional tank of Philips 66 or 76 and the 93 octane when I find it. The Coupé always runs Great! My Brother and I have been runnin’ around the Bay Area lookin’ for TV’s all week, (want one of those Wide Screen LCD HighDef TV’s for the Motorhome) I’ve been doing All the driving. My Bro wants to fill the Coupés tank but he wants to with some discount fuel, (Rotten Robbie) I protest but as there’s no Chevron around and I’ve been shelling out near $40 a tank he breaks me down.

~ The Coupé Runs Like SH!T! ~ Rotten Robbie is Right! She’s Sputtering, Idling Rough and Revving High!? Take my foot of the brake pedal and She Takes Off!!?? Her Fuel Mileage is Nil. Exhaust Smells Bad. If I Rev Her Real-High a few times She’ll kick down to normal idle for a while. Service Engine Light comes up now and then but get this, NO CODES! Not a single one! "Service Engine" has Always resulted Codes. This morning I have 4 gallons left so I burn most of it off Hauling Azz to my Bro’s. I Bitch about it all the way to my Favorite Chevron for a Bottle of Techroline and a Tank of Supreme. I Haul Azz up the 85 to 880 to 101. Now She’s Runnin’ like the Dream She is! This isn’t the first time this has happened, I’ve been out of town in need and had to take what I could get with these same results!? Anyone else experience this? Guru’s, do you have any thoughts?

Skullman {:{}

Thats funny. I have a 90 seville with the 4.5 that will burn anything. I then bought a 90 deville that has to have premium or it runs like crap.

Blaze

hahaah my 4.1 will burn anything too, i guess she just appreciates having gas in her at all lol

Thats funny. I have a 90 seville with the 4.5 that will burn anything. I then bought a 90 deville that has to have premium or it runs like crap. Blaze then shredder130 Opined hahaah my 4.1 will burn anything too, i guess she just appreciates having gas in her at all lol

~ Hey Boils & Goils: Just to make it Clear, only Premium "ETHYL" Runs the Veins of the Coupé! I find that this Problem I seem to have with Her is not very much different then my Harley. NUMNUTS (My Bike) has a Few Modified Squirrels in her, She's Breathin' a Lot better, Compression has been Upped, though Squish and the way it was achieved had to be taken into account. Because of this I don’t have to be as finicky with fuel for her. We have a few Beamers in the family and they don’t seem to be as finicky with Fuel in their Higher Compression Engines. Though the 4.1, 4.5 and 4.9 are Sisters, there are Significant Differences! Hell, I can Run anything in the Boat Anchor of an Engine in my Motorhome (Ford 460) same goes for the El Camino!

{:{}

The folks I got my 90 Coupe DeVille (4.5) from always ran 87 in it but they only putted around town with it and babied it everywhere they went.. when I drove it home with the 87 stuff the couple WOTs I did didnt ping and it pulled smoothly. But I filled her up with 91 right away as I have a mucho heavy foot. So some depend on how you drive her I guess.

~ The Coupé Runs Like SH!T! ~ Anyone else experience this? Guru’s, do you have any thoughts? Skullman {:{}

~ OK, I’m going to quote myself, again. Guru's do you have any thoughts!? I can't be the only 4.9 Owner that has experienced this? Are our 4.9’s that Touchy with the Fuel they Ingest? Quality or as I perceive to be Quality Fuel is the only thing the Coupé wants to consume with-out any Major Balking! Hey, bbobynski I would think that you may have come across something like this in your travails through your motorized knowledge!? What do you say? I’ve Never had a Rig that was this sensitive to quality of fuel. My Bro has a ’96 STS and that Northstar has seen some questionable fuel and always runs like a top! At first I thought it might just be an unusual bad batch of fuel but as time goes by I’ve seen a pattern of problems with fuel from the discount fuel distributors!? Maybe I need to De-Tune the Coupé to except these “Questionable” Fuels? Yeah Right! What exactly is at play that would make the engine Idle High, Run Rough, Stumble, Kick on the Check Engine Light and Not throw any Codes? Only to Clear Up with a Tank of "Quality Fuel"!?

Skullman {:{}

Octane is the only difference. They tune these engines to run on 91. They could of tuned them to run on 87 but did not. There are reasons but the fact is they are tuned for 91. The 05 Mustang 300hp performance engine is tuned for 87 and runs fine. 91 does nothing for it. Some have taken the 05 and reprogramed the computor to run on 91 and they now need that. Shaved some time off the quarter mile. As far as anything else other than octane Mobil, Sunoco, Shell. rotten robbie all come from the same spicket at your fuel terminal. Each vendor then adds some chemicals as it flows into the tanker. So you most likely see a performance difference but that's the octain, nothing else.

The 4.9 does not have a knock sensor so it will not tolerate low octane fuel as well as a Northstar. You didn't mention what octane "discount fuel" you used. I had a '92 4.9 and always used discount fuel (and still do) and I have never had a problem. Maybe you just got a bad tank full (water in the fuel). Try a different discount station and see it the problem repeats itself. I'd bet it won't.

This thread strikes me with an interesting question. I have a '97 Deville w/ N*. I *ALWAYS* put Shell or BP Ammoco (non discount places) 93 Octane fuel in it. The dash tells me to use Premium fuel only. Is this just some horeshit or what? I hate paying 40$ to fill it up, but hell if thats what I gotta do, thats what I gotta do.

This thread strikes me with an interesting question. I have a '97 Deville w/ N*. I *ALWAYS* put Shell or BP Ammoco (non discount places) 93 Octane fuel in it. The dash tells me to use Premium fuel only. Is this just some horeshit or what? I hate paying 40$ to fill it up, but hell if thats what I gotta do, thats what I gotta do.
Try this, document your mileage, mpg and fuel cost per mile, for a few tank fulls of the premium gas you have been running, then switch to a lesser grade for a few tank fulls. It shouldn't hurt your system, if you think is is, switch back, but you should see with the third tank, wether there is a difference.

Kev